Maintaining genome integrity and epigenetic programming is essential to avoid disease and retain the identity and proper function of the multitude of specialized differentiated cell types in the body. Much progress has been made in the past 10 years toward identifying and understanding the range of proteins and complexes involved in these processes. Many of these are chromatin-remodeling complexes, including those that contain the Williams syndrome transcription factor (WSTF). This protein is particularly interesting for two reasons. First, it functions in many central nuclear processes, such as DNA replication, transcription, and DNA repair. Second, WSTF is haploinsufficient in Williams-Beuren syndrome (WBS) patients. This is because the WSTF gene, BAZ1B, is deleted, along with approximately 27 other genes, from one copy of chromosome 7 in affected individuals. Prior research has implicated WSTF in contributing to several of the phenotypes exhibited in WBS, yet many aspects concerning the function of WSTF remain unclear. A more detailed understanding of WSTF function is necessary to appreciate how this versatile protein contributes to general nuclear processes, and how perturbation of these roles contribute to the symptoms displayed in WBS patients. This study examines the function of WSTF in several ways. First, this research identifies and characterizes the relationship between WSTF and heterochromatin, with a particular focus on facultative heterochromatin of the human inactive X chromosome (Xi). Next, it describes the generation of human cell lines that either lack or are happloinsufficient for WSTF through the generation of heterozygous and homozygous mutant BAZ1B alleles. Using these invaluable model cell lines, this research explores the impact of WSTF reduction or loss on several processes, including heterochromatin maintenance, the DNA damage response, and vitamin D induced gene expression. This work reveals that WSTF is necessary to maintain appropriate expression of a substantial number of genes, and describes a novel nuclear phenotype in BAZ1B knockout cells, characterized by the spontaneous formation and subsequent resolution of extensive regions of heterochromatin throughout the nucleus. This research contributes to and extends current understanding of WSTF function, and provides BAZ1B knockout cells to further investigate WSTF mechanism, as well as providing BAZ1B heterozygous knockouts that will serve as a model to examine how WSTF haploinsufficiency contribute to WBS in the absence of the effects of the other 27 genes that are typically deleted in the disorder. Analyses found in this dissertation link WSTF function to maintenance of chromatin and transcriptional states. Through the examination of BAZ1B knockout cells, this work also underscores that the current understanding of WSTF is not as clear as anticipated, given that processes expected to be disrupted in the absence of WSTF were unaffected. This dissertation concludes with a discussion of these findings as well as future implications.
